In power equipment like various transportation vehicles, industrial and mineral machinery, etc., an engine is one of the most commonly used in these equipments. In the traditional reciprocating engine, crankshaft linked to the piston via a connecting rod transforms the linear motion into the rotation of the shaft. Because the directions of linear motion are frequently changed in the reciprocating motion, great inertial loss of components of the reciprocating engine, such as pistons, connecting rod, and the like, would occur when changing the directions. In addition, during the movement of the piston in the cylinder, the lateral pressure generated by the friction between the piston and wall of the cylinder acts on the piston continuously, resulting in power loss of the piston.
Chinese utility model patent CN2076164U discloses a wobble engine comprising a cylinder block, a cylinder liner, a cylinder head, a piston, a camshaft, an inlet and exhaust device, a spark plug, an output shaft and an actuating device, characterized in that the cylinder block has a cylindrical shape which is divided into a plurality of cylinders by the cylinder head; a spindle is positioned in the center of the cylinder block and is surrounded by the arched cylinder liner; the copying piston is positioned into the cylinder liner in which the piston pole is fixedly connected with the spindle. When the cylinders are in operation, the power attained by of the spindle in wobbling motion of the piston in the cylinders makes the output shaft always moved in the same direction through an oriented ratchet and pawl mechanism.
Compared with the conventional linear reciprocating engine, this structure has been greatly improved so that the oscillation and the noise of the whole structures as well as the wearing capacity in respect to the roundness are reduced, because the main components of this engine make the concentric wobbling motion. But because the wobbling motion is merely a partial circumferential motion, there still exists the problem of changing the directions of the piston. Thus, dynamic loss resulting from the change of the directions would be unavoidable. Furthermore, the components forming the wobbling motion render the center of gravity of the engine to be unbalanced axially. As a consequence, there still exist various drawbacks in this structure.
Chinese utility model patent CN2402803Y discloses a rotary engine having an arched cylinder-piston, which comprises a piston-cylinder mechanism, a stopping mechanism for piston, a pendulum mechanism for piston, an inlet and exhaust mechanism, a fuel oil-supplying mechanism and a cooling mechanism, characterized in that the cylinder, the piston and the piston ring take the shape of arched cylinder. The cylinder is connected with a spindle in a key manner through the cylinder arm and is rotated synchronously with the spindle. The piston is in a relative reciprocating motion in the cylinder and moves round the spindle only in the same direction through the piston arm, not in reverse. Because no crankshaft is provided in this invention, the direction of pressure exerted by the gas on the piston is perpendicular to the rotating radius of the piston all along, thereby greatly improving the useful power in order to operate in high speed, operate smoothly and reduce the wear. However, because the piston is still in a relative reciprocating motion in the cylinder, the power loss generated by change of the directions of the movement of the piston is not resolved yet.
In view of the drawbacks of the structures in the prior art, the speed of conventional reciprocating engine can is difficult to be further increased. Also, the engine has the problems of poor balance, greatly reduced efficiency, and so on.
Furthermore, although a Wankel engine does not have a problem relating to crankshaft and has advantage of inertia, it also has the following deficiencies presently: high fuel consumption, serious air-pollution due to the discharged waste gas, serious wear of metal, etc, thus it is not popularized and needs to be further improved.